Indexable insert for thread cutting and slotting

ABSTRACT

In thread cutting and slotting, indexable inserts of hard metal are now used. Usually, the inserts used have been of triangular type. In order to improve cutting economy, implying improved positioning, closer tolerances, and increased strength, an insert (1) has been developed for use in, for example, internal thread cutting, said insert (1) being formed with two cutting edges (2, 2&#39;) on a bevelled cutting body (1, 3). Since the cutting body (1) is located on a cutting column (10), the cross section of which is symmetrical, the insert with the cutting body (1) and the cutting column (10) may be reversed half a turn with essentially retained directional geometry. The insert (1, 10) has a plurality of plane guiding and contact surfaces (5, 5&#39;, 6, 6&#39;, 14, 14&#39;) adapted to match the corresponding plane guiding and contact surfaces in an insert holder (13) in order to achieve correct positioning of the indexable insert in the insert holder.

The present invention relates to indexable inserts for thread cuttingand slotting to be used, for example, in internal thread cutting ofworkpieces by means of automatically controlled machine tools.

PRIOR ART

There are different methods of making threads and slots, involvingeither plastic machining or machining by means of cutting of a blank of,for example, screw or nut type. The most frequent method for producingthreads for screws, bolts and nuts is plastic machining by means ofthread rolling, in which the thread profile is pressed into the surfaceof the material. Machining by means of cutting comprises the followingmethods: use of threading taps and threading dies, thread milling,grinding and chasing. In thread chasing, the thread is cut into therotating workpiece by means of a tool edge such as a cutting insert,suitably of indexable type, clamped in an insert holder. With modern NCand CNA lathes/machine tools, threads can be made quickly andefficiently using cutting inserts and holders for same. The counterpartof the thread cutting of a workpiece is an ordinary turning operation,in which the feeding per revolution corresponds to the thread pitch. Thepointed end of the indexable insert is usually cut to a profile intendedto correspond to, for example, the space between two thread sides. Thechip cutting thickness is determined by the cutting depth. The feedingmovement of the tool must be related to the rotary movement of the workspindle. Often, a feeding function as such is provided in the lathe. Anoperator or a computer monitors and controls the actual threading.

Indexable inserts for thread cutting and slotting have been available onthe market since the early 1960s. Mainly, triangular cutting inserts ofpositive or negative cut type have been used for horizontal as well asvertical mounting in the insert holder. There are certain disadvantagesassociated with a cutting insert of this type, since it may be difficultto locate the insert accurately in the holder and there is a risk ofinsert rupture. As a result of the development as regards equipment,greater demands have to be made as to locating tolerances, and improvedbuilt-in safety as regards insert rupture must be demanded, especiallyin view of the use of unmanned converting machines in continuousoperation. Owing to the large investments in equipment required today,cutting economy has become an issue of ever greater importance tocompanies.

DESCRIPTION OF THE INVENTION

In order to improve cutting economy, the indexable insert according tothe invention for internal thread cutting and slotting is provided withtwo cutting edges at the ends of a bevelled cutting body. A cuttingcolumn with symmetrical cross section relative to an axial sectionthrough the central axis of the column is connected with the cuttingbody, thus allowing the cutting insert to be reversed half a turn, ifrequired, for continued use of the cutting insert. The cutting columnhas a plurality of limiting surfaces with parallel intersecting lines,which contributes towards great accuracy as regards location andorientation when mounting the cutting insert in the holder. With thisdesign, much closer tolerances are possible than in the case of othertypes of cutting inserts. Owing to the cutting body between the cuttingedges having been given an elongated shape, the cutting forces will acton the cutting insert within a larger angular area as compared toprevious solutions, and the forces and the heat will be absorbed moreefficiently in the whole of the cutting insert including the cuttingbody and column, whereby the risk of a cutting insert rupture isconsiderably reduced. Further, since the cutting body supports twocutting edges in a line which can be ground at the same time, animprovement in production technique is achieved.

DESCRIPTION OF THE FIGURES

FIG. 1 shows different views of a cutting insert comprising a cuttingbody and a cutting column according to the invention, FIG. 1A being alongitudinal side view, FIG. 1B being a longitudinal side viewperpendicular to FIG. 1A, and FIG. 1C being a top view of the insert.

FIG. 2 is an end view of the cutting insert mounted in the holder.

FIG. 3 shows a side view and a top view of the insert holder and cuttinginsert FIG. 3A being a longitudinal side views of the insert from oneside, and FIG. 3B being a longitudinal side view perpendicular to FIG.3A.

FIGS. 4 and 5 are respective bottom and top perspective views of thecutting insert of FIGS. 1-3.

DESCRIPTION OF AN EMBODIMENT

A cutting insert according to the invention comprises a cutting column10 and a cutting body 1 of hard metal connected with the cutting column.The cutting body (head) 1 supports a bevelled portion 3 with two cuttingedges 2 at each end, the cutting edges being oriented in oppositedirections. The bevelling angle and shape was chosen in consideration ofthe profile to be cut. Adjacent the cutting edges 2, the cutting body isprovided with chip breakers/deflectors 4, 4'. Inside the cutting edgeswith the bevelled portion 3 of the cutting body 1 there is an end face8. Between the guiding edges 9, 9' of the cutting body 1 and the cuttingcolumn 10 there are intermediate bevelled/inclined guiding and contactsurfaces 14, 14' for accurate angular adjustment and positioning of theinsert 1, 10 relative to the corresponding guiding and contact surfacesof the insert holder 13. The cutting column 10 is provided with aplurality of longitudinally disposed guiding and contact surfaces 5, 5',6, 6' with parallel intersecting lines, these guiding and contactsurfaces together with the corresponding guiding and contact surfaces ofthe insert holder also contributing towards the correct positioning ofthe insert 1, 10. With all these guiding and contact surfaces of theinsert and the holder, positioning of the insert can be made veryaccurately, at the same time as the shape of the insert with thebevelled cutting head and the two cutting edges makes it possible tolocate the cutting edges differently by reversing the insert withretained accurate positioning. By inclining the insert in the holder(see FIG. 2), for example 15° relative to a workpiece, both the upperand under side of the cutting head, i.e. both cutting edges, may be usedin the machining of a workpiece. For holding the insert 1, 10, theinsert holder 13 is provided with a slot 15 which delimits a tab portion16. The outer end of the insert holder 13 and the outer end of the tabportion 16 are provided with guiding and contact surfaces matching thecutting column 10. In the tab portion there is a conical bore 17 intowhich a suitable screw head will fit and which is concentric with athreaded bore 12 in the insert holder.

By means of a screw 11, such as a socket head cap screw, the insertedcutting insert on tightening is clamped between the tab portion 16 andthe lower part 18 of the insert holder.

What is claimed is:
 1. A hard metal indexable insert for thread cuttingor slotting and which is reversibly insertable in an insert holder, saidinsert comprising a column and a cutting head at one end of said column,said column defining flat outer guide surfaces along a length thereofand said cutting head defining first and second pairs of opposite sidefaces and an end face, each side face of said first pair of oppositeside faces defining a peak guiding edge and a contact surface portionwhich extends from said shaft to said peak guiding edge, and said endface defining first and second end surface portions and a bevelled,elongated protrusion therebetween, said bevelled, elongated protrusionextending across said end face between said first pair of opposite sidefaces and defining cutting edges at opposite ends thereof.
 2. Theindexable insert of according to claim 1, wherein said column has ahexagonal cross section, thus defining six flat outer guide surfaces;wherein said faces of said second pair of opposite faces of said cuttinghead are flat, and wherein a pair of opposite flat outer guide surfacesof said column are coplanar with said flat faces of said second pair ofopposite faces of said cutting head.